1. Field of the Invention
The present invention relates to a method of and a apparatus for measuring stress in a semiconductor material and for automatically measuring internal stresses of a thin film formed on a surface of a semiconductor substrate such as a silicon wafer or the like and fine processing parts variously patternized, which is incorporated into a manufacturing line of a semiconductor device or the like as a method of inspecting a product and a product material.
2. Description of Related Art
In a semiconductor device manufacturing process, quality control through the measurement of stresses of a thin film formed on a surface of a semiconductor substrate such as a silicon wafer or the like and fine processing parts of different patterns, a film thickness, a composition and the like is an significantly important and indispensable element for maintaining a stable performance of the manufactured semiconductor device.
In particular, in the semiconductor device, a complementary CMOS circuit is used in order to realize a high-performance large scale integrated circuit (LSI) in a sub 100 nm region, and it is very important to realize a higher speed in the CMOS circuit. As a technology for realizing the high-speed CMOS circuit has been developed a manufacturing technology for the semiconductor device in which strained silicon having a carrier motility larger than that of a conventional silicon is used. The technology is aimed at improving the carrier mobility in such manner that a silicon layer is formed on a silicon germanium layer (including SiGe layer recited below) having a large grating constant, and a tensile strain is applied to the silicon layer (thin film) so as to modulate a silicon band structure.
In the technology of the strained silicon, the quality control, which includes the measurement of the internal stress of the SiGe layer, let alone the measurement of a stress state of the strained silicon layer, and preferably, the control of the film thickness of each layer, the measurement of a germanium (Ge) content in the SiGe layer and the like, plays a very important role in improving the productivity of the high-performance and high-speed semiconductor device.
In general, Raman spectroscopic technology is adopted for measuring the stress of the semiconductor material such as silicon. To describe the stress measurement using the Raman spectroscopic technology, it is generally known that, for example, a peak position of the Raman spectrum is shifted by approximately 1 cm when the stress of 0.5 φ Pa acts on a single crystal silicon, and the shift of the peak position of the Raman spectrum is utilized to estimate a stress at a measurement point based on the change of the peak position of the Raman spectrum.
In order to apply the stress measurement by the Raman spectroscopy to the foregoing strained silicon to thereby obtain a highly accurate measurement result and measurement reproducibility for maintaining the highly accurate measurement result in a stable manner for a long period of time, it is vital to constantly control a shift amount of the peak position of the Raman spectrum to approximately 0.01 cm. However, the shift of the peak position of the Raman spectrum in accordance with variations generated in an optical system by changing ambient temperature, examples of which are a wavelength shift caused by a minor strain of any optical component and a temperature change of the semiconductor material itself as a measuring object (for example, in the case of the single crystal silicon, the peak position shifts by approximately 0.02 cm when the temperature changes by 1° C.), is inevitable. Therefore, when the generally available Raman spectroscopic technology is directly applied to the measurement of the stress of the strained silicon, it becomes very difficult to assure a predetermined measurement accuracy and measurement reproducibility.
In order to deal with the problems mentioned above in measuring the stress of the strained silicon using the generally available Raman spectroscopy, a conventional method, in which a plasma line of a gas laser is fetched along with the Raman light (scattered light generated by the irradiation of an excitation light) and a shift amount of a peak position of the plasma line is used to correct the peak position of the Raman spectrum so that the stress is measured based on the corrected peak position of the Raman spectrum, was proposed (for example, see No. 2001-66197 of the Publication of an Unexamined Japanese Patent Application).
Further, as a technology for measuring the internal stress of a material such as semiconductor using Raman spectroscopy, a stress evaluation method, in which a temperature of a material to be measured at a measurement point is changed, a plurality of peak wave numbers of the Raman spectrum variable in response to the temperature change are measured, and the plurality of measurement values (peak wave number) are subjected to a statistical processing at each measurement point so that data free of any influence from the temperature change of the measured material itself at the measurement point can be obtained, was proposed (for example, see No. H06-82098 of the Publication of the Unexamined Japanese Patent Application).
As shown in FIG. 3, a semiconductor material 3 using strained silicon as a typical measuring object is formed from, for example, serially providing a SiGe layer 3C of several 10 nm-several 100 nm and a strained silicon layer 3D of several nm-several 10 nm in a multilayer structure on a single crystal silicon substrate 3A via a silicon oxide layer (hereinafter referred to as SiO2 layer) 3B. The semiconductor material 3 having the multilayer structure is constituted in such manner that the stress does not act on the substrate 3A itself in the presence of the SiO2 layer 3B between the single crystal silicon substrate 3A and the SiGe layer 3C. Therefore, the Raman spectrum of the substrate 3A at the time of irradiating an excitation light from the direction of the strained silicon layer 3D is in a non-stress state, which can lead to the conclusion that the shift, if any, generated in the peak position of the Raman spectrum of the substrate 3A results from the influence of the temperature change of the measured semiconductor material 3 itself.
Further, it is important to select a wavelength of the excitation light, on which a penetration depth of a light largely depends, in measuring the Raman spectrum of the semiconductor material 3 using the strained silicon. Of Ar lasers typically used for the Raman spectroscopy, an Ar ion laser having the wavelength (λ) of 514,488,457 nm, which is an oscillation beam having a relatively large intensity, penetrates at the depth of 760,560,310 nm, and an He—Cd laser having the wavelength (λ) of 325 nm penetrates at the depth of approximately 10 nm. Therefore, in the case of measuring the Raman spectrum using the excitation light generated by the Ar ion laser having the wavelength of 514 nm and large penetration depth, as shown in FIG. 6, the Raman spectrum having a large intensity can be detected due to a Si—Si band (peak wavelength) in the SiGe layer 3C, while the Raman spectrum of the Si—Si band in the strained silicon layer 3D cannot be detected under the influence of the Raman spectrum of the substrate 3A. Therefore, it is necessary to use a ultraviolet light such as an He—Cd ion laser having the wavelength of 325 nm in order to unfailingly detect only the Raman spectrum of the strained silicon layer 3D which is the uppermost layer.
On the other hand, when the laser having a small wavelength and a small penetration depth is used, the excitation light does not reach the SiGe layer 3C, which makes it impossible to measure the Raman spectrum of the SiGe layer 3C. Therefore, it becomes necessary to use a visible light having a long wavelength as the excitation light in order to measure the Raman spectrum of the SiGe layer 3C or the substrate 3A.
While it is possible to avoid any influence from the changing ambient temperature by controlling the variations of the optical system caused by the change of the ambient temperature by means of the conventional method recited in No. 2001-66197 of the Publication of the Unexamined Japanese Patent Application in the case of measuring the Raman spectrum of the strained silicon layer 3D using the ultraviolet light as the excitation light, the influence received from the temperature change of the measured semiconductor material itself easily results in the generation of a large error in a predetermined stress measurement. Therefore, in the pursuit of assuring a highly accurate measurement undergoing fewer errors and stable measurement reproducibility in a long period of time, a temperature adjusting mechanism for maintaining the temperature of the semiconductor material at a constant degree or the like and a number of additional steps are unfavorably required in order to avoid any influence from the temperature change of the measured material itself. The additional steps are, for example, a specimen for correcting the temperature is prepared apart from the semiconductor material to be measured and a spectrum of the correction specimen is measured prior to the measurement of the semiconductor material so that the peak position of the Raman spectrum influenced by the temperature change of the semiconductor material is corrected based on the measurement information and the predetermined stress measurement can be thereby implemented.
In the case of the conventional method recited in No. H06-82098 of the Publication of the Unexamined Japanese Patent Application, a large number of steps and a resultant large amount of time are required for measuring the stress of even one material to be measured in order to obtain a highly accurate measurement result eliminating any influence from the temperature change of the measured material itself. The required steps are, for example, the temperature is changed at each of the plurality of measurement points, the plurality of peak wave numbers of the Raman spectrum variable in response to the temperature change are measured, and the plurality of measurement values (peak wave number) are subjected to statistical processing at each measurement point. As a result, a remarkable deterioration of a productivity is triggered by incorporating the measurement of the stress of the semiconductor material having the foregoing disadvantages into the manufacturing line in which a high speed and continuity are demanded, such as the manufacturing of the semiconductor device. Thus, it is practically not possible to introduce such a stress measurement. In addition, the conventional method serves to correct the change of the peak wave number of the Raman spectrum due to a temperature difference resulting from the different configurations of the respective components when the excitation light is irradiated on a single material as a measuring object and does not respond to the influence from the temperature change of the entire material to be measured. As described, the conventional method included such problems that the measurement accuracy was inevitably lowered due to the shift of the peak position of the Raman spectrum in accordance with the temperature change of the measured material itself and the measurement reproducibility could not be assured in a long term.
The present invention was implemented in order to solve the foregoing problems, and a main object is to provide a method of and an apparatus for measuring the stress of the semiconductor material requiring neither the temperature adjusting mechanism for maintaining the temperature of the semiconductor material at a constant degree nor any additional step and capable of performing the predetermined stress measurement with a high accuracy and at a high speed irrespective of the changing ambient temperature and the temperature change of the material itself.